1. Field of the Invention
This invention relates to musical tone generation devices, and in particular, to musical tone generation devices used for synthesizing and generating musical tones that stimulate the sound of wind instruments, plucked string instruments, rubbed string instruments, and struck string instruments.
2. Prior Art
Electronic musical tone synthesizers using FM (frequency modulation) tone generators are conventionally known. This type of musical tone synthesizer generates an envelope whose amplitude varies over time by means of an envelope generator. This envelope controls tone color amplitude and pitch of musical tones.
Additionally, musical tone synthesizers wherein tone generation is accomplished by simulation of the sound generation mechanism of conventional non-electronic musical instruments have been recently proposed. This kind of musical tone synthesizer consists of a closed-loop circuit incorporating a low-pass filter which simulates the acoustic decay and a delay circuit which simulates the propagation delay of vibration in a conventional non-electronic musical instrument. With this type of tone generator, an excitation signal such as an impulse signal is provided to the closed-loop circuit, wherein the excitation signal circulates.
When above described type of musical tone synthesizer is used to simulate a stringed instrument, the excitation signal circulates within the closed loop once in a duration equivalent to a vibration period of a string in the conventional stringed instrument. The bandwidth of the circulating signal is limited by the low-pass filter. Finally, the circulating signal is extracted from this closed loop and is used as a musical tone signal.
Control of the above described excitation signal can be accomplished by using, for example, an envelope pattern output from an envelope generator. In Japanese Patent Laid-open No. Sho-63-40199 and Japanese Patent Publication No. Sho-58-58679, musical tone synthesizers have been disclosed incorporating a closed loop circuit of the type described above, and wherein the excitation signal supplied to the closed loop is controlled using an envelope pattern output from an envelope generator. An example of volume control in this type of device will be described with reference to the waveform diagrams shown in FIGS. 6(a) and 6(b). FIG. 6(a) shows an envelope pattern output from an envelope generator which is applicable to volume control and the like for musical tones under ordinary circumstances. In FIGS. 6(a) and 6(b), the vertical axis indicates the output level of the envelope generator and the horizontal axis indicates time. During simulation of a conventional non-electronic instrument, volume control can be suitably carried out using an envelope pattern wherein the output level is initially zero after which it rises to a level of one, and then decays back to a level of zero, as is the case with the example shown in FIG. 6(a). Additionally, the pattern shown in FIG. 6(b) could suitably be applied to volume control during simulation of a wind instrument. In the case of the envelope shown in FIG. 6(b), the output level at the initial attack is somewhat greater than zero, but otherwise, the pattern is essentially the same as the pattern shown in FIG. 6(a).
However, the above described devices for simulating the sound generating mechanisms of conventional non-electronic musical instruments are in certain respects inadequate for simulating many types of instruments. Specifically, multiple differing control parameters must be provided at predetermined times for predetermined intervals when simulating, for example, a wind instrument. In fact, even for a relatively simple envelope pattern such as that shown in FIG. 6(b), generation of the necessary control parameters in the specified sequence is a considerably complicated problem, to which conventional devices such as those described above are not well suited due to bandwidth limitations, processing speed and other factors.
Furthermore, envelope patterns supplied from the envelope generator in the type of musical tone synthesizer described above produces a response having hysteresis properties similar to those shown in FIG. 7. Thus, when simulating a wind instrument, for example, when simulating increasing blowing pressure, the volume response is that described by the lower curve in FIG. 7, whereas when simulating decreasing blowing pressure, the volume response is that described by the upper curve in FIG. 7. Thus, the volume level corresponding to a given blowing pressure differs depending on whether the blowing pressure is increasing or decreasing. For this reason, there is a large difference between the envelope pattern supplied from the envelope generator and the musical tone actually generated, making it difficult to control the sound volume in a linear manner.
Also, depending on the extent of the hysteresis, sound generation may be perceived as having a delay following a key-on event because the initial volume is abnormally attenuated. This problem is particularly aggravated at low volumes, such that the generated sound may be imperceptible long after tone generation has commenced.